This invention relates generally to a steam generator plant. More particularly, the present invention relates to a steam generator plant that is connected to a multistage steam turbine and that has a fluidized-bed combustion system, with this system having a fluidized-bed combustion chamber, at least one second gas pass and at least one separator positioned between the fluidized-bed combustion chamber and the second gas pass, at least one superheater, and two reheaters connected in series on the steam side, with the first reheater being constructed with a regulated bypass mechanism on the steam side, so that a partial flow of the steam that is fed to the second reheater can be directed past the first reheater, and it also relates to a procedure for the operating of such a steam generator unit.
In a power-plant facility that uses a steam generator, the energy content of a fuel is used for the evaporation of a working medium or flow medium within the steam generator. In this connection, the working medium is usually conveyed within an evaporator circuit. The steam made available by the steam generator can in turn be provided, for example, for the driving of a steam turbine and/or for an attached external process. If the steam drives a steam turbine, then via the turbine shaft of the steam turbine usually a generator or a machine for doing mechanical work is operated. In the case of a generator, the current produced by the generator can be provided for purposes of feeding it into an interconnected and/or insular network.
Moreover the steam generator unit can be constructed to have a fluidized-bed combustion system, especially a circulating fluidized-bed combustion system. Such a steam generator unit has become familiar, for example, from the printed document EP 0 455 660 B1. This steam generator unit, which is a component of a power plant with a multistage steam turbine, includes a fluidized-bed combustion system that has a fluidized-bed firing, at least one separator, at least one initial and one second stage or final stage of the reheater, which are connected in series, and a superheater. In this connection, the first and the second stage or final stage of the reheater are positioned in series within a common gas channel or a second gas pass of the steam generator, which is connected on the gas side with the fluidized-bed combustion chamber, and also elements are provided for dividing up the steam which comes from the high-pressure section of the steam turbine and which has been expanded in part, into a selective first and second portion, and for a leading of this same first portion through the first stage of the reheater, and elements for re-uniting the first and second portion and a leading of the same through the second stage of the reheater. By means of the above-mentioned arrangement, the steam temperature at the outlet of the reheater system can be regulated without an injection of colder injection water. This elimination of injection water has a positive effect on the overall efficiency of the power-plant facility.
In this familiar steam generator unit, it has proved to be a drawback that the reheater (Zxc3x9c) temperature characteristic is not optimal and thereby the case can arise where the Zxc3x9c temperature of the steam to be heated is not reached at partial load. Furthermore, the number of heating surfaces in the second gas pass has an effect on the overall height of this gas pass. Due to the fact that two reheater heating surfaces are provided in the gas pass, the overall height of the second gas pass is correspondingly greater and more costly.
The object of the invention, then, is to create a steam generator unit as well as a procedure for operating a steam-generator unit of this species, in which unit and in which procedure the above-mentioned drawbacks can be avoided.
The above-stated object is attained with respect to the steam generator unit by the characterizing features of Patent claim 1, and with respect to the procedure by the characterizing features of Patent claim 8.
Through this achievement in accordance with the invention a steam generator unit as well as a procedure for operating such a unit is created that has the following advantages:
An improvement of the temperature characteristic of the reheater system or of the reheater stages and with that a lower heating-surface requirement. Since the second reheater is arranged within the fluidized-bed combustion chamber, a number of advantages result from this. For one thing, the flue gas (RG) temperature is higher in the combustion chamber compared to the flue-gas temperature in the second pass, and this results in a higher driving temperature difference for the heat transfer to the steam in the second reheater, and as a consequence of this the heating surface needed is smaller. In this connection, it is especially advantageous that in the fluidized-bed combustion chamber, because of the high solid-particle portion in the flue gas the RG temperature is almost constant over the entire height of the second reheater. For another thing, in the fluidized-bed combustion chamber, in addition to the convection heat acting on the reheater stage a greater fraction of radiant heat is added, and this radiant heat is considerably more independent of the boiler load than the convection heat and moreover at partial loads its release of heat flux to this heating surface is reduced to an only insignificant degree. Through the above-named measures, the Zxc3x9c temperature characteristic is considerably improved.
Through the improved temperature characteristic of the reheater in the combustion chamber, smaller bypass flows past the first reheater are needed. Due to the greater flow through the first reheater, a better cooling is achieved. Furthermore, due to the smaller bypass flows, now also the bypass mechanism can be made smaller and at a lower cost.
Through the reduction (elimination of the second reheater stage) of the heating surfaces (heat-recovery area or convection heating surfaces) in the second gas pass, the overall height of the second gas pass can be kept smaller and it can be made at a lower cost.
It is advantageous for the second reheater of the steam generator unit to be constructed as a platen-type heating surface, since thereby the heat transfer to the steam working medium takes place through both convention and also radiation.
The platen-type heating surface of the second reheater in the fluidized-bed combustion chamber can be constructed in the shape of an L (wing walls). This shape can considerably simplify the installation and the linkages of the respective heating-surface tubes. But it can also be conveyed horizontally through the fluidized-bed combustion chamber.
It is particularly advantageous for the steam generator unit to be constructed with a regulation mechanism including at least one flow-rate regulating valve for the dividing up of the steam flow into a partial flow directed through the first reheater and possibly a partial flow directed through the bypass line, where the regulation takes place as a function of the steam temperatures at the inlet and outlet of the first reheater as well as the steam temperatures at the inlet and outlet of the second reheater. By means of this measure an extremely efficient and precise regulation of the steam temperatures in the individual reheater stages is achieved.
From a control-engineering point of view it is advantageous for the flow-rate regulating valve to be constructed as a 3-way valve and to be positioned at the bifurcation to the supply line to the first reheater and to the bypass line. But it can also be expedient to construct the flow-rate regulating valve as a simple straight-through valve and to position it in the bypass line.
In another advantageous embodiment of the invention, in connection with a procedure for the regulation of reheater temperatures in steam generator units of this species, the regulation of the steam flow directed through the first reheater and of the steam flow optionally directed through the bypass line takes place as a function of the steam temperatures at the inlet and outlet of the first reheater as well as of the steam temperatures at the inlet and outlet of the second reheater.